The invention relates to a bypass filter unit, in particular, for filtering supplies of hydraulic oil in a bypass flow, comprising a motor-driven pump and a fixedly mounted filter housing closeable by a cover and containing an exchangeable filter element.
In a large number of cases, the bypass filter units defined at the outset are used for cleaning supplies of hydraulic oil in hydraulic systems in order to clean the supply of hydraulic fluid outside of the working flow of the hydraulic fluid. The hydraulic fluid, in particular, the hydraulic oil, is taken from the oil supply, conveyed through the bypass filter unit, filtered and returned as clean oil to the hydraulic oil supply.
These bypass filter units can also be used for transferring hydraulic fluids by pumping (e.g. filling a hydraulic tank from a barrel).
In addition to the technology explained hereinabove with an exchangeable filter element, a second form of bypass filter unit operating with so-called spin-on filters, in which the filter element and the filter housing form one unit, has established itself.
In both technologies, however, the problem of changing the filter has been solved in an unsatisfactory way, in that either dirt particles deposited on the filter element are able to get back to the clean oil side or large quantities of hydraulic fluid have to be discarded on both the clean oil side and the dirty oil side when the filter is changed. In both cases, the handling of the filter elements, whether it be the filter elements as such, which are exchangeable, or the spin-on unit consisting of filter element and filter housing, involves a lot of work and often enough causes soiling of the environment with oil.